1. Field of the Invention
The present invention relates to apparatus for obtaining images of a scene using a single imaging device, wherein the images can be displayed as a three dimensional illusion of the scene when viewed by an observer having monocular vision.
2. Prior Art
The production of two-dimensional images that can be displayed to provide a three-dimensional illusion has been a long standing goal in the visual arts field. Methods and apparatus for producing such three-dimensional illusions have to some extent paralleled the increased understanding of the physiology of depth perception.
The perception of three-dimensional space depends on various kinds of information (cues) in the scene being viewed, such as relative size, linear perspective, interposition, light and shadow, gradients (monocular cues), as well as retinal-image size, retinal disparity, accommodation, convergence (binocular cues), and familiarity with the subject matter of the scene viewed (learned cues).
The most important binocular cue is parallax, i.e., depth information gain from comparing the images of the scene from each eye. The distance between the center points or irises of the eyes of an average human being, generally referred to as the intraocular distance or disparity, is approximately 65 mm. The fundamental physiological basis for binocular vision is two eyes that look in the same direction and have overlapping visual fields. Each eye views a scene from a slightly different angle and focuses it onto the retina, a concave surface at the back of the eye lined with nerve cells, or neurons. Because the retinal surfaces are two-dimensional, the images focused by the eyes are also two-dimensional. Both two-dimensional images are transmitted along the optic nerves to the brain's visual cortex, where they are combined, through stereopsis, to form a three-dimensional model of the scene. The rate of combination in the brain of the two-dimensional images formed at the retina, generally referred to as the viseo-psychological suppression or memory rate, appears to be approximately 3 to 6 Hz.
Various approaches have been used in the past to obtain and display images having the appearance of depth. One commonly used approach is to obtain images of a scene from two horizontally displaced viewing points of origin. The horizontal displacement of the points of origin is generally equal to or less than the intraocular distance. Images obtained from these two points are simultaneously superimposed on a projection screen, but the light forming these images is polarized differently for the images from the left point of origin than for images from the right point of origin. Accordingly, it is necessary for the observer to wear glasses having appropriately polarized lenses. Because of the necessity of having to wear these special glasses, this stereoscopic approach to displaying images in three-dimensional illusion has never gained wide viewer acceptance.
Consequently, development efforts have concentrated on an autostereoscopic approach to displaying images in three-dimensional illusion, which does not require the viewer to wear special glasses. In this autostereoscopic approach, images from horizontally displaced left and right points of origin are displayed alternatingly rather than simultaneously. An example of this approach is disclosed in U.S. Pat. No. 4,303,316 issued to McElveen. U.S. Pat. No. 4,006,291, issued to Imsand, adopts a form of this approach in which images from one point of origin are primarily used, while images from another point of origin are periodically inserted.
More recently, autostereoscopic approaches using vertical alignment of the viewing points, generally referred to as vertical parallax, have been proposed. An example of a vertical parallax system is disclosed in U.S. Pat. No. 4,429,328, issued to Jones, Jr., et al. Studies have shown that the vertical parallax approach to autostereoscopic imaging produces the appearance of depth, while being more amenable or comfortable to the viewer than the horizontal parallax approach.
The use of separate cameras, one at each of two points of origin, to record images which are then displayed in alternating fashion is disclosed in U.S. Pat. No. 4,966,436 issued to Mayhew and Prichard. While this approach produces images which provide a three-dimensional illusion upon when displayed, precision matching of chrominance and luminance of the two cameras is required. Moreover, considerable operator skill is required to adjust disparity, convergence and time-displacement rates of image recordings in a coordinated manner to maintain a stable image.
To avoid the drawbacks associated with a two camera system, autostereoscopic methods and apparatuses using a single camera/single lens have been developed. U.S. Pat. Nos. 5,014,126 and 5,157,484, also issued to Mayhew and Prichard, disclose single camera autostereoscopic systems capable of recording images which, when displayed, are perceived by a viewer in three-dimension.